1. Field of the Invention
This invention relates to a closure device comprising a frame provided with at least one flow-through passage, a closure means mounted displaceably for each passage, and a counter part formed in the frame for each closure means. The closure means is displaceable between an open position, which permits a normal air flow, and a closed position, which may be caused by a pressure shock, in which the closure means is pressed against the counter part so as to close the respective passage.
2. Description of the Prior Art
Shelters for apparatus and people are usually provided with some kind of a ventilation system. In order to provide effective protection against an explosion taking place outside the bomb shelter, the ventilation system has to comprise a closure device or valve which prevents a pressure shock caused by the explosion from entering the shelter. The closure device or valve has to close immediately as a result of the pressure shock caused by the explosion; on the other hand, it has to stay open under normal conditions to allow the exhaust and supply of air.
In the most commonly used structures the closure means is formed by an axially displaceable disc or a pivotable flap. In such devices, the pivoting or sliding movement of the closure means also causes sliding or torsional friction, which may prevent a disturbance-free operation of the device due to wear and dirt.
In another device known in the prior art, the frame of the device is provided with flow-through openings, whereby a rodlike closure means is provided for each opening. The closure means are supported by springs so as to be fixed with respect to the frame. Due to the fixed spring system, the inherent rolling movement of the cylindrical closure means is prevented. In addition, spring systems have such general disadvantages as the fatigue, wear and corrosion of the springs.
Attempts to avoid disadvantages of spring systems in structures of the above kind have been made by substituting springs with the force of gravity; however, a steady disturbance-free operation thereby seems questionable.